1. Field of the Invention
The invention relates to a multimode fuel injector for combustion chambers, in particular the combustion chamber of a jet engine. More particularly it concerns the cooling of the annular distribution chamber fed by the secondary circuit and which communicates with a plurality of fuel ejection orifices ensuring the peripheral atomisation of the fuel delivered by the secondary circuit.
2. Discussion of the Background
In an aircraft jet engine, the combustion chamber is equipped with a plurality of fuel injectors distributed at regular intervals along the circumference at the back of the latter. Each fuel injector comprises an arm in which are defined coaxial passages belonging to a fuel circuit, called primary and a fuel circuit called secondary respectively. Each coaxial passage, defined inside the arm, feeds two coaxial fuel atomisation systems, defined in the same atomisation head.
The primary circuit or low engine speed circuit is designed to obtain particularly fine fuel atomisation. Its flowrate is limited but permanent.
The secondary circuit or high engine speed circuit is designed to supplement the fuel flowrate up to the point of full throttle making it possible, in particular, to attain all the power necessary for takeoff. On the other hand, this secondary circuit is not used permanently and its flowrate is sometimes very weak at certain engine speeds.
As an example, EP 1 369 644 describes a multimode fuel injector of this type.
The compressed air coming from a high pressure compressor circulates in the casing where the combustion chamber is located. Part of the air crosses the fuel injectors, mixes with the fuel delivered by the primary and secondary circuits at the back of the combustion chamber, before igniting in the latter.
The fuel injector can be subjected to high temperatures (300° K to 950° K for power at full throttle) since it is installed in a flow of hot air coming from the last stage of the high pressure compressor. Moreover, during certain phases of operation where the temperature of the air from the compressor is relatively high (430° to 630° K), the secondary circuit may not be used or may have a very weak flowrate.
Gumming or coking could result from the fuel stagnating inside the atomisation head and more particularly inside the annular distribution chamber feeding the various fuel ejection orifices providing peripheral atomisation. These phenomena can impair the quality of atomisation of the fuel supplied by the secondary circuit and cause non-homogeneous carburetion in the combustion chamber as well as a distortion of the map of the temperatures inside the latter. This can result in a loss of performance of the combustion chamber and the high pressure turbine. These problems may cause burning of the high pressure distributor, high pressure turbine and even certain components of the low pressure turbine.